Propionic acid synthesis



Patented Aug. 29 19 39 v UNITED STATES rATEN'r OFFICE.- 2,110,925 a PROPIONIO ACID SYNTHESIS Donald J. Loder, Wilmlngj lssignor to E. I. du Pont do Nemoln's & Oonmany, .Wllmington, Del, a corporation of Delaware Ne Drawing. Application January-27, 193s,

SerlalNo. 187,226 r 8. Claims. (Cl. 280-532) This invention relates to an improved process ethyl chloride, and the like, may likewisebe used. for the preparation of propionic acid and its although due to its availability, low cost, and esters and particularly to the preparation of proadaptability I prefer to employ ethanol as the pionic acid by theinteraction of ethanol and carmajor raw material.

bon monoxide in the presence of boron fluoride An aqueous solution of boron trifluoride is pre- 5 as the catalyst. J ferred as the catalyst, which may be made in var-.

An object of the invention is to provide a ious ways such, for example, as by the solution process for the preparation of propionic acid in of boron trifluoride in water; by the interaction exceedingly high yields from ethanol and carbon of anhydrous'hydrogen fluoride with boric oxide 0 monoxide. A further object of the invention is or boric anhydride; or, if desired, by the introto provide a process for preparing propionic acid duction of boron trifluoride'as a gas directly into and its ethyl ester irom ethanol and carbon mon-. the mixture of water, ethanol, ether and/or ester oxide in the presence of such proportions of water prior to or during the reaction. Other boron fluand boron trifluoride that substantially 100% oride compounds may be employed which contain conversion of the'ethanol ,to acid and/or ester boron, fluorine and water such, for example, as 15 is obtained. Yet another object of the invention aqueous solutions of dihydroxyfiuoboric acid, is to provide operating conditions for the aforeborofiuohydric acid, and, in general, the oxygenmentioned process under which substantially no ated acids obtained from mixtures -of hydrogen undesirable lay-products are formed during the fluoride and the boric acids.

no reaction. Other objects of the invention will Aqueous solutions of boron trifluoride,as well 0 hereinafter appear. as the other enumerated catalysts are preferably I have found that propi'onic acid and its ethyl used alone, although agents may be added to proester can be prepared .in exceptionally high yields mote the activity of these catalysts, if desired, from carbon monoxide and thanoL'pr v dins such as free'hydrofluorlc acid, powdered nickel,

boron fluoride is employed as the atalyst in enickel oxides, or other powdered metals or meta1'2ii 1 359 of Suitable amounts o Water and under oxides. Generally, however, I have found it prefthe proper temperature conditions. General y. erable to use aqueous boron trifluoride alone, for

it may be. stated that my improved process init is not only easily prepared but is sucha powervolves carrying out the propionic acid synthesis iui catalyst that further modification by the ad- #0 y correlation of boron trifiuoride conce a dition of other substances is not ordinarily nec- 80 water concentration and temperature in order essary I V that the reaction is eifected rapidly and without A ar ful study of th th p a b the formation of condensation products heretooxide t propionic acid reaction has revealed that tone inva ia encountered when ethanol or it is desirable to have presentsufllcient water to a other higher alcohols have been condensed with inhibit t formation. of by pmducts and m 35 carbon monoxide, particularly in the presence of and I have determined t t it is advantageous boron h l nn catalysts to. have at least mol of water present per mol The ethanol-carbon monoxide reaction to of t n y preferably 1 t 3 mols r water which this invention-is particularly directed may per mol of t alcohqL w t has ,th pro... 40 'be expressed as f ll w nounced efl'ect oi raising convertsiori stc propimtig 4o acid from'50-70% when no wa er presen C2H5OH+COfiC2H5COOH 90-100% when there are one or more 'mols of In accordance wi h the particular operat ng 0011- "water. The boron trlfluoride should be present ditlons, it will be found that in some instances for optimum operating conditions in the ratio propionic acid may not be formed as the acid, but of from 1 to 4 mols per mol of the ethanol and 45 may e produced as th ste y condensati n preferably between 2 and 3 mols of boronfluoof theacid with the ethyl alcohol used in the ride per mol of ethanol; and, for some purposes, p ess s ndi a ed e o I solutions saturated with borontriflioridedmgg be used. "I'heseconcentrations o wa er an ran CZH5COOH+QZH5OH6C2H5QOOC2HE+H2O trifiuoride appear to be unique for the synthesis 50 The ethanol used may be replaced, if desired, of ,prop'ionic acid and give exceptionally high wholly or partly by diethyl ether or esters of proyields if temperature conditions are properly picnic acid, principally ethyl propionate. Furs controlled. These conditions can advantageously thermore, compounds which'decompose upon hybe used also in the reaction 'of carbon monoxide 5K drolysisto give ethanol such, for example, as: with alcohols'suchas propanol, normal and isobutanol, and, generally higher than methanol, higher organic acids.

For improved operation I have found that when the above concentration of water and boron trifluoride are employed the synthesis should preferably be carried out at temperatures below 180 C. down to approximately 125 C. with preferred temperatures ranging between 185 and 165 C. The pressureshould likewise be maintained, for optimum results, above 25iatmospheres and preferably between 500 and 1000 atmospheres,

The carbon monoxide used may be obtained from various commercial sources such, for'example, as from water gas, producer gas, coke oven gas and the like, but to obtain products with the highest degree of purity it is preferable to remove from such commercial gases objectionable speaking, all alcohols tor the preparation of constituents.

. stances, desirable.

} Furthermore, inert gases may be present in the carbon monoxide used and they are, in some in- Nitrogen, for example, has, it appears, little deleterious effect on the reaction or yield and, in fact, it may be used advanta geously in order to aid in the agitation of the reactants, particularly if the carbon monoxide is to be bubbled through them. Other strictly inert gases will usually actsimilarlyto nitrogen.

While the above description has been directed particularly to the reaction of carbon monoxide with ethanol, diethylether, and/or ethyl propi0nate;'I have found that generally the higher alcohols will react similarly to give higher acids. Normal .and isopropyl alcohol will give isobutyric acid; normal butyl alcohol will give methyl ethyl acetic acid; isobutyl alcohol will give trimethylacetic acid'and the higher alcohols,corres'pond-.

'ing higher acids.

When carrying out my process with the higher alcohols, I have found it to be generally true that best results are realized when the reaction is conducted at temperatures below 180 C. down to 125 135 and165 C.

The moredetailed practice of the invention is illustrated by the following examples in which parts are given by weight unless otherwise stated. There are, of course, many forms of the invention other than these specific embodiments.

f Example 1 .A silver-lined autoclave was charged with 806 C. and preferably between parts'of a mixture containing. on a molal basis,

' admitted in a shaker machine between 138 and 154 1 part of ethanol, 1.8.parts of water, and 2.8 parts of boron trifluoride. The autoclave was heated to a temperature ranging C. It was heated to reaction temperature within 28 minutes and main- Throughout the reaction a pressure of 800 to 900 atmospheres was maintained by the periodic introduction of carbon monoxide as it was absorbed. 8'71 parts of product was discharged which, upon -analysis, gave a yield'based upon reactants used acid and 10% of propionic Egarr ipl e ethyl propionate.

- A ,sil'ver lined autoclave was evacuated and subsequently tu're containing, on a molal basis, 1 part of ethanol,'0.5 part of water and 1.5 parts of boron trifluoride. Compressed carbon monoxide was then to 'raise the pressure to approximately 300 atm'ospheres. With the tube agitated, the chargwwas then heated" within 24 minutes to a temperature between-140 and 152 C. The prespropionate and 85% partsof product were analysis, gave a yield of 92% propionic acid.

charge of 684 parts of 800 and 900 atmospheres.

charged with 692 parts of a mix! 7 sure increased during heating to between 500 and 900 atmospheres. The temperature was maintained within the indicated range for 3'7 minutes and whenever the gas absorption caused the pressure to fall to 800 atmospheres the pressure was raised again to 900 atmospheres by introducing carbon monoxide from high pressure storage. At the end of .the 37-minute reaction period, gas absorption substantially ceased. The autoclave was cooled and 7'75 parts of product discharged. Upon analysis the product was found to contain a yield based on reactants used of 6.6% of ethyl of propionic acid.

Example 3 The process of Example 2 was repeated using a charge containing 624 parts of a molal mixture of 1 part diethyl ether, 4.6 parts of water and 4 parts of boron trifluoride. The temperature was raised in 45 minutes to from 150.to 160" C. and maintained in this range for 60 minutes with a pressure between 800 and 900 atmospheres. 732 discharged which, upon Example 4 The process of Example 2 was repeated with a charge containing 764 parts of a molal mixture containing 1 part of ethanol, 1.8 parts of water and 2.7 parts of boron trifluoride. These reactants were raised within 32 minutes to a temperature ranging between 144 and 158 C. and maintained at that temperature for approximately 60 minutes. tion, was held between 816 parts of product were discharged which, upon analysis, gave a yield'of 70% propionic acid.

Example 5 The-process a mixture containing, on a molal basis, 1 part of ethanol, 1.8 parts of water, and 2.4 parts of boron trifluoride. This-mixture was raised to a temperature between 135 and C. in 26 minutes, maintained at that temperature for 39 minutes, during which apressure was held between 800 and 900 atmospheres. 842 parts of product was discharged which, upon analysis, gave a yield of approximately 98% propionic acid.

Emmplefi The process of Example 2 was repeated with a charge of 742 parts of a mixture, on a molal basis, 1 part of ethanol, 0.0'7 part of diethyl ether, 1.8 parts of water and 2.86 parts of boron trifluoride. This mixture was. raised to a tem-.

perature between 141 and 151 maintained at temperature for during this period the pressure was held between 807 parts of, product was discharged which, upon analysis, gave a 100% yield of propionic acid.

The crude product from the synthesis contains water, boron trifiuoride, propionic acid and, under certain operating conditions,. ethyl propionate and hydrocarbons. The recovery of the acid and. ester, from this crude product may be efiected by first removing that portion of theboron fluoride which is readily vaporized by merely heating the product. As it is desirable to recover the boron fluoride driven. off during this stage of the recovery, a packed tower, condenser and absorber for the boron "fluoride are-provided, the latter containing preferably water. The residue from this step is steam distilled to recover the propionic acid and ester. The residual water and C. in 31 minutes,

The pressure, during this reac-v 250 and 300 atmospheres.

of Example 2 was repeated with a 24 minutes and boron fluoride may be treated in coon! with processes described in Ser. Nos. 54,329 and boron fluoride in substantially tom.-

10 I claim:

1. A process of produeiiil acid which comprises reacting ethihol with cirflon iiii'ihoxiderin the presence of boron fluoride and water; 'as the catalyst, at a temperature betteen 125 C.

and, 180 0., and at a pressure in eaeeu or 25 \atmospheres. v V 2. Process of claim I conducted With a racial ratio of boron fluoride 1. i 20 3. Process oi claim 1 oonpiucted with 3- 15a: ratio of boron luoflde to efliahol frbinfi to 3 parts of boron fluoride to 1 part of 4. The proceae otJclaim I conducted with a remime . l toethtfloloi'l'reaterthali 3 what mixture substantially saturated with boron triiluoride. 111

the bree'ence or water is the catalyst. peratlire betweeii 125? Qfand 180 C., and pressures in exce'ga oi';25 atmospheres.

8, A for the preparation of propionic which absorbing carbon monoxide 35 C. and 165 G'Qond under a pressure between '800 anflfloflmtfm'ofilzeres.

. DONALD J. LODER. 

